The present invention relates to air-moving fans, and is more particularly directed to centrifugal fans or blowers associated with heating, ventilation, and air conditioning (HVAC) equipment. The invention specifically concerns an improved scroll or air guide for directing the air from a centrifugal fan or blower. In a specific embodiment described hereafter, a covered split scroll is beneficially applied to a packaged terminal air conditioner (PTAC) but would also be appropriate for room air conditioners or other devices.
A packaged terminal air condition (PTAC) is a unit having an indoor or interior side connected to an outdoor or exterior side through a penetration in a wall of a building. These units can be used both in summer as an air conditioner for cooling, and in the winter for heating. The PTAC generally can often employ the same motor and drive shaft to power the outdoor side and a centrifugal fan on the indoor side.
It has long been a goal in the industry to increase the air moving efficiency of these fans, both to reduce the electrical power requirement and also to reduce the noise level generated by the fan.
The centrifugal blower on the indoor side of the PTAC or other similar unit normally has a so-called scroll or flow guide to conduct the exhaust air from the blower out to an air plenum at the top front of the unit. Centrifugal fans generally require a scroll to diffuse and collect the air flow efficiently. In most HVAC systems, the air flow is discharged into a downstream system, which can be a duct, a collection of furnace heatexchanger cells, a plenum, or a variety of blockages and turns. Control of relatively high-velocity air exiting the fan is critical if pressure loss (and hence, noise) are to be minimized.
In PTAC units, relatively high velocity air leaves the centrifugal fan, is redirected upwards by the scroll, is discharged into a deck cavity or plenum, and then negotiates a ninety degree turn to exit the front of the unit. One way to reduce noise from a PTAC unit would be to enclose the noise source. The centrifugal fan in the PTAC unit is the dominant indoor noise source, but total enclosure is not feasible because of the necessity for an air inlet and for air outlet ducts. However, a logical compromise would be partial enclosure of the fan or blower to eliminate any line-of-sight noise radiation.
Another approach to noise reduction involves minimizing air pressure requirements imposed on the fan, that is, increasing air moving efficiency. This would permit a lower pressure-rise fan, and hence a quieter fan, to replace the existing fan without loss of air handling capacity.
However, prior to this invention, no suitable adaptation has been proposed for centrifugal blowers.